The invention relates to Voice services over Adaptive Multi-user channels on One Slot (VAMOS) receivers, and more particularly to techniques for improving the performance of a VAMOS receiver.
Voice capacity is doubled in the Global System for Mobile Communications (GSM) system by means of “Voice services over Adaptive Multi-user channels on One Slot” (VAMOS) technology, whereby two orthogonal subcarriers are transmitted in the same time-slot. The sub channels are separated by using non-correlated training sequences. The use of orthogonal subcarriers can considerably increase voice capacity with low impact to handsets as well as to networks. The concept may double the traditional capacity of the GSM system, for example, a double half rate channel providing that 4 users can be allocated to the same radio slot.
In the receiver side (e.g., mobile station), specialized architectures are made use of to achieve better interference cancellation and to separate out the desired orthogonal subcarrier channel's data. Conventional receiver architectures employed in a VAMOS phase2 (“VAMOS-2”) receiver are:
1. Successive interference cancellation (SIC) receiver.
2. Joint demodulation (JD) receiver.
Comparing the performance of these conventional receivers, one finds that a joint demodulation receiver outperforms the successive interference cancelation receiver by about 3-5 dB. However, the joint demodulation receiver is computationally complex to implement, and this is a serious drawback especially in a mobile station (mobile receiver). Hence, successive interference cancellation is a preferred choice for mobile receivers.
For at least the foregoing reasons, it is desirable to have improved VAMOS receiver technology (e.g., methods, apparatus) having sufficiently low complexity to make it a good choice for use in mobile receivers, while exhibiting improved performance over its conventional counterparts.